VAR
 n,i:word;
 r,s:real;
 x,y:array[1..100] of real;

 function dlina(x,y,x2,y2:real):real;
 begin
  dlina:=sqrt(sqr(x-x2)+sqr(y-y2));
 end;

BEGIN

 readln(n,r);
 for i:=1 to n do readln(x[i],y[i]);

 for i:=1 to n-1 do
  s:=s+dlina(x[i],y[i],x[i+1],y[i+1]);

  s:=s+dlina(x[n],y[n],x[1],y[1]);

  s:=s+2*pi*r;

  writeln(s:0:2);
  readln;
END.


